The present invention relates in general to storage tanks, and, more particularly, to tank integrity protection means.
Storage tanks are used to store many types of materials, such as liquids which include cryogenics, petroleum products, or the like. These tanks can assume extremely large sizes and the liquid tanks can contain millions of gallons of product.
A failure of such liquid tanks can be catastrophic if tank failure is complete. A brittle fracture mode failure of a metal LNG storage tank has been postulated by some members of the LNG industry. Such a fracture has been envisioned as causing the storage tank to be cleaved along all or part of the height thereof. Such a fracture would result in a large opening in the side of the tank through which the stored product would escape. The escaping product would produce a considerable impact load on the wall of a secondary container located outside the primary storage tank. Also, the primary storage tank could be thrust against the wall of the secondary container causing a second, considerable impact. This second impact load would be centered 180.degree. from the first impact load.
Provision of massive walls for secondary containers, or supporting such secondary container walls with an earthen berm are not satisfactory solutions to a problem of adequately protecting a storage tank against a brittle fracture mode failure such as the above-discussed failure. These solutions are not cost efficient, and are not reliable enough to warrant the costs involved therewith.
The assignee of this patent application owns U.S. Pat. No. 3,861,552, issued Jan. 21, 1975, disclosing hoops provided around a tank for providing added structural capability to the tank, wherein the tank hydrostatic pressures require providing plate material thicknesses which require field stress relieving. Such hoops are a part of the tank structure, that is, the hoops and/or other such supports are not structurally isolated from the tank wall. As a result of the structural coupling between the tank wall and the reinforcing means, the stressing forces exerted on the tank wall are transmitted to the reinforcing means, and any cracks appearing in the tank wall may propagate into that structure intended to reinforce the tank wall. The tank wall is thus still susceptible to a catastrophic failure.
Thus, there is need for efficient means for protecting a storage tank against failure by limiting the size of a wall crack.